Fluids frequently become contaminated during use and must be purified before they can be recycled. For example, lubricants, hydraulic fluids, transformer oils, and cutting fluids often become contaminated with water, cleaning solvents, or other volatile contaminants which must be separated from the fluids before the fluids can be reused.
A variety of fluid purifiers have been previously designed based on the use of heat or vacuum or both to separate a volatile contaminant from a fluid. One problem with previous fluid purifiers is providing sufficient purification in a single pass through the purifier without harming the fluid itself. Purifiers with harsh processing conditions, such as excessive heat or excessive vacuum, may provide sufficient purification in a single pass, but they often have destructive effects on the fluids being purified. For example, the fluid can be seriously altered through the loss of low boiling point components, removal of additives, or oxidation or charring of the fluid.
Purifiers with milder processing conditions, such as lower temperature or lower vacuum, may not harm the fluid being purified, but they often provide only partial purification in a single pass. The fluid must be pumped through the purifier many times for sufficient purification. This multi-pass approach substantially increases the amount of energy and time needed to purify the contaminated fluid.
A problem with previous fluid purifiers based on the use of a vacuum is producing a large enough surface area for a given volume of fluid to allow sufficient release of the contaminant. There is less resistance to the release of volatile contaminants at or near the surface of the fluid than within the body of the fluid. Insufficient surface area results in only partial purification, again making it necessary to pump the fluid through the purifier many times before the fluid is sufficiently purified.
Another problem with previous vacuum purifiers is that their performance varies substantially with the viscosity of the contaminated fluid. These purifiers usually use some medium, such as a downward flow column, to form a thin film of the contaminated fluid which increases the surface area of the fluid. If the fluid is viscous, however, it forms a thick film. The release of volatile contaminants from the body of the thick film is a much slower process which increases the time required to purify the fluid.